1. Field of the Invention
The present invention relates to a picked-up image signal processing apparatus and a picked-up image signal processing method both of which convert a subject image into an image signal and process the image signal as a luminance signal and color-difference signals.
2. Description of Related Art
Conventionally, in a picked-up image signal processing apparatus which is arranged to convert a subject image into an image signal and process the image signal as a luminance signal and color-difference signals, the image signal is processed by signal processing blocks such as those shown in FIG. 13.
A received light image of a subject is converted into an electrical signal by a CCD 1. The electrical signal is converted from its analog form to a digital form by an A/D conversion circuit 2. The obtained digital signal is processed in both a color processing system 51 and a luminance processing system 52.
In the color processing system 51, a color interpolation circuit 3 receives the digital signal outputted from the A/D conversion circuit 2 and outputs four complementary color signals of yellow (Ye), cyan (Cy), magenta (Mz) and green (G) for each pixel of the CCD 1. These complementary color signals are converted into pure color signals of red (R), green (G) and blue (B) by a matrix circuit 4, and are outputted therefrom as RGB signals. Then, a gamma correction circuit 6 matches the RGB signals to a video signal to be visually displayed on a television monitor or the like, and a color-difference matrix circuit 7 converts the RGB signals supplied from the gamma correction circuit 6 into color-difference signals. After that, a color suppression circuit 20 eliminates color noise from a low luminance portion of each of the color-difference signals and also suppresses the color of a pixel of the CCD 1 which pixel contains a high luminance color.
In addition, the bands of the color signals are limited by the series of processing blocks of the color processing system 51 such as the color interpolation circuit 3. Specifically, the color signals contained in the digital signal outputted from the A/D conversion circuit 2 are subjected to band limiting processing by the color processing system 51, and are then converted into the color-difference signals.
In the meantime, in the luminance processing system 52, a color carrier elimination circuit 8 eliminates a color carrier component from the digital signal outputted from the A/D conversion circuit 2, thereby forming a luminance signal which is almost unprocessed. Then, an aperture correction circuit 10 raises the characteristic of a high band portion of the luminance signal. A gamma correction circuit 11 performs gamma correction on the thus-corrected luminance signal similarly to the gamma correction circuit 6 in the color processing system 51. After that, a luminance color-difference correction circuit 9 corrects the balance between color components in the luminance signal by using the color-difference signals color-suppressed by the color suppression circuit 20 of the color processing system 51, and outputs a final luminance signal.
In the conventional signal processing apparatus, the color suppression circuit 20 color-suppresses the color of a saturated pixel of the CCD 1 which pixel contains a high luminance color.
However, if the CCD 1 receives a light image of a subject of high luminance and a pixel of the CCD 1 is saturated, the influence of the saturated pixel of the CCD 1 is liable to spread over its surrounding pixels through the processing performed by a series of processing blocks such as the color interpolation circuit 3 of the color processing system 51. During the reproduction of the subject image on a television monitor or the like, the image quality of a final output image may be degraded by a false color which differs from the color of a subject, not only in a high luminance portion of the final output image but also over the surroundings of the high luminance portion.
In addition, since color suppression processing is performed at a final stage of the color processing system 51, it is necessary to execute color processing on the surroundings of the high luminance portion to prevent the degradation of image quality, so that the circuit scale of the color processing system 51 increases.
If the above-described color suppression is performed, the surroundings of the subject are color-suppressed, so that the color information of the final output image may be lost to cause degradation of its image quality.
Furthermore, the frequency band of a signal for detection of a saturated high luminance portion of the CCD 1 differs from those of color-difference signals to be color-suppressed, and if the frequency band of a signal for detection of a high luminance portion is narrower than those of color-difference signals to be color-suppressed, it may be impossible to color-suppress a correctly saturated pixel.